Griffiths Phase and Reduced Magnetization of La0.5Ca0.5MnO3 with Different Annealing Temperature

In this paper, the existence of Griffiths phase and variation of ferromagnetism have been studied for La_0.5Ca_0.5MnO₃ nanoparticles annealed at different temperatures. It is detected by x-ray diffraction patterns that the increasing of annealing temperature induces the increment of grain size. The magnetization as a function of temperature demonstrates that magnitude of magnetization at low temperature is decreased as the annealing temperature increases, which is explained by the core-shell model. The temperature dependence of inverse susceptibility of those samples manifests that the Griffiths phase occurs for the samples annealed at temperatures 900?°C and 1150?°C and it disappears for the sample annealed at 1350?°C. The reduction of Griffiths phase with increasing of annealing temperature indicates the suppression of quenched disorder after annealing, which may be related to the lower degree of disorder, redistribution of magnetic ions, and weaker hybridization of?O?2p states with its near-neighbor atoms. As to the disappearance of Griffiths phase, competition between paramagnetic, ferromagnetic, and antiferromagnetic phases plays a very important role.